A wide variety of additives have been developed and are in commercial use for the protection of metals against corrosion in organic or aqueous media.
Amongst ferrous metal corrosion inhibitors, carboxylic acids are widely used, for example, those with long chain alkyl or aryl groups which impart solubility to the carboxylic acids in organic systems, for example hydrocarbon oils. Particularly effective compounds are acyl amino acids of structure (I):R1—C(O)—N(R2)—CH2—CO2H  (I)where R1 is a long chain alkyl group and R2 is hydrogen or methyl.
Where water solubility is required, it is common practice to employ a water soluble salt of the carboxylic acid, for example, a sodium salt or a trialkanolamine salt. Amongst non-ferrous metal corrosion inhibitors (also known as metal passivators or deactivators), the most widely used compounds for protection of copper and copper alloys are triazole derivatives, particularly benzotriazole or tolutriazole. As above, derivatives are well known which enhance solubility in organic hydrocarbons or water. For example structures of formula (II) are in commercial use:T1—CH3—NR32  (II)where T1 is a triazole derivative, R3 is hydroxyalkyl (for water solubility) or alkyl (for oil solubility).
When ferrous metal and non-ferrous metal corrosion inhibition are both required in an oil-based medium two oil-soluble corrosion inhibitors are used. Similarly, when both ferrous metal and non-ferrous metal corrosion inhibitors are required in an aqueous medium, two water-soluble corrosion inhibitors are used.
However, in a number of applications, solubility of the corrosion inhibitor in both organic hydrocarbons and water is desirable. Such applications include, but are not limited to, those involving emulsions or those where water may be present as a contaminant of oil styrene and vice versa. Applications where dual solubility would be of utility include, but are not limited to, industrial oils, crankcase lubricants, metalworking fluids, hydraulic fluids, rolling oils, brake fluids, fuel systems, surface coatings and water-soluble paints.
In an effort to reduce the amount of organic hydrocarbon material used in many technologies, aqueous emulsion formulations are being developed so that the range of technical areas in which emulsions will have importance is increasing. However, the conventional corrosion inhibition compounds described above result in either organic solubility or water solubility.
It is an aim of preferred embodiments of the present invention to provide an improved corrosion inhibitor.